Process for the reproduction of information by short-duration,high-intensity exposure of a heat-sensitive material to visible light



May 12, 1970 VRANCKEN ETAL 3,511,652

PROCESS FOR THE REPRODUCTION OF INFORMATION BY SHORT-DURATION,

HIGH-INTENSITY EXPOSURE OF A HEAT-SENSITIVE MATERIAL I'O VISIBLE LIGHT Flled June 15, 1966 2 Sheets-Sheet 1 FIG. 1

INVENTORS WOLFGANG LA'ss/e MARCEL NICOLAS VRANCKEN WA TSON. COLE. GRINDLE & WATSON ATTORNEYS May 12, 1970 v Nc ETAL 3,511,652

PROCESS FOR THE REPRODUCTION OF INFORMATION BY SHORT-DURATION,

HIGH-INTENSITY EXPOSURE OF A HEAT-SENSITIVE MATERIAL TO VISIBLE LIGHT F'iled June 15, 1966 2 Sheets-Sheet 2 J g j INVENTORS WOLFGANG L A SSIG MARCEL NICOLAS VRANCKEN WATSON, COLE, GRINDLE 8 WATSON ATTORNEYS United States Patent PROCESS FOR THE REPRODUCTION OF INFOR- MATION BY SHORT-DURATION, HIGH-INTEN- SITY EXPOSURE OF A HEAT-SENSITIVE MATERIAL TO VISIBLE LIGHT Marcel Nicolas Vrancken, Hove, Belgium, and Wolfgang Lassig, Cologne-Stamrnheim, Germany, assignors to Gevaert-Agfa N.V., Mortsel, Belgium, a Belgian com- Int. Cl. case 5/04 US. CI. 96-27 5 Claims ABSTRACT OF THE DISCLOSURE Difiiculties normally encountered in thermographically copying multi-colored originals due to the differing absorption of infrared radiation by the different colors are avoided by using a thermographic copying material 1ncluding a layer having uniformly incorporated therein a substance which absorbs visible radiation and converts the same to heat and filtering the radiation impinged upon the original to remove at least a major portion, and preferably substantially all, of the infrared radiation therefrom. Preferably, the radiation is emitted by a flash lamp having a very brief exposure. A thermographic material having in heat-conductive relation with the radiation absorbing-converting substance a heat-sensitive layer composed essentially of particles of hydrophobic thermoplastic polymer dispersed in a hydrophilic binder gives particularly good results.

The present invention relates to a process for the production of copies by a brief intensive exposure, especially by reflex exposure, the copying material being exposed to light comprising substantially no infrared radiation.

When producing copies according to the so-called flashexposure process, as described e.g. in the French patent specification 1,312,209 or according to the reflex printing method, as described e.g. in the Belgian patent specification 657,502, unsatisfactory results are sometimes attained since depending on the image colour of the original different copies are reproduced with a different quality or if a copy shows different colours, the image parts with the different image colours are reproduced differently.

In the copying materials commonly used for the flash exposure technique the different character of the colours manifests itself in the form of an over-exposure or an under-exposure. 'Ihen e.g. the materials described in the above-mentioned patent specifications are used, which materials are coloured and change their colour at the exposed areas, it is impossible on exposing them to an original containing lines of different colours to reproduce these lines with the same width.

It has been found now that excellent copies can be produced according to the flash-exposure process, especially by reflex exposure, by using for the exposure of the heat-sensitive materials a copying light that comprises no or almost no infrared radiation.

This object is accomplished easily by placing an infrared-absorbing filter in the path of rays between the original and the copy. The filter may consist of suitable glass plates adsorbing infrared radiation or cells containing a liquid e.g. an aqueous copper sulphate solution adsorbing infrared radiation.

As copying materials those described in the abovementioned French patent specification 1,312,209 and 3,511,652 Patented May 12, 1970 Belgian patent specification 657,502, can be used for carrying out the process according to the invention. These materials are characterised in that they are insensitive to normal daylight but change colour by the local heating brought about by the flash-exposure at the exposed areas. The apparatus described in the Belgian patent specification 664,868 is particularly suited for the processing of the materials according to the invention. The infrared I filter can be used separately or in the form of a filter layer applied to the heat-sensitive material. Preferably, the filter is substantially transparent to radiation 'with wavelengths below 800 In.

Other suitable copying materials for use in the flash exposure technique are described in Belgian patent specifications 656,713 and 674,869 respetcively and in the specification of Marcel Nicholas Vrancken et al., US. application Ser. No. 550,834, filed May 17, 1966. Suitable materials according to the latter Belgian patent specification comprise a recording layer wherein an imagewise change in solubility or permeability for water or aqueous solutions is obtained by heating. Particularly suitable are the heat-sensitive materials, which are insensitive to daylight and comprise at least one layer having incorporated therein particles composed wholly or mainly of a hydrophobic thermoplastic polymer as a dis persion in a hydrophilic binder in a ratio greater than 1:1 by weight, these particles being in heat-conducting relationship with one or more substances, which absorb electromagnetic radiation in at least a part of the wavelength range of said radiation and convert the corresponding part of said radiation into heat.

EXAMPLE 1 Production of the infrared filter A 120 thick gelatin foil is soaked for 10 minutes in a 20% aqueous copper sulphate solution and dried. The absorption curve of the foil is represented by the curve A in FIG. 1. During the exposure this foil is placed between the light source and the heat-sensitive material.

Production of a heat-sensitive copying material 30 (see FIG. 2)

A composition consisting of 900 g. of a 10% aqueous gelatin solution, 30 g. of a 12% aqueous solution of saponine, and 30 g. of a 2.5% aqueous solution of the sodium salt of the condensation product from oleic acid and methyltaurine is applied on a cellulose triacetate foil 31 pro rata of 50 g. per sq. m. the cellulose triacetate foil 31 being coated previously with a gelatin subbing layer 32. After solidification, the resulting material is coated with a heat-sensitive layer 33 pro rata of 36 g./sq. M. from the following composition:

G. 10% aqueous solution of gelatin 5O 40% aqueous dispersion of poly(ethylene) having a particle size of 0.1a and an average molecular weight between 15,000 and 30,000 Water 320 60% aqueous dispersion of carbon 4 5% aqueous solution of sodium tetradecylsulphate 40 The material is then dried with an air-stream. at 30 C.

Subsequently, the heat-sensitive copying material 30 is exposed reflectographically to an original 34 comprising coloured image parts by means of a xenon gas discharge lamp 35. The exposed material is slightly Wetted with water and then with its heat-sensitive layer 33 pressed against a receiving paper. The material and the receiving paper are conducted between two pressure rollers at a travelling speed of approximately 10 cm./sec., one of the rollers being heated to 35 C. When emerging from between the rollers, both materials are immediately peeled apart. A thin stratum of the heat-sensitive layer 33 is transferred image-wise to the receiving paper so as to form a legible print in accordance with the original 34.

EXAMPLE 2 Production of the infrared filter A composition consisting of 50 g. of gelatin, 8 g. of Prussian blue, and 450 g. of water is applied to a gelatincoated cellulose triacetate support pro rate of 50 g. per sq. m. The resulting material is dried. The absorption curve of the material is represented by the curve B in FIG. 1, the ordinate indicating the absorption and the abscissa indicating the wavelengths.

The filter is used in the same manner as described in Example 1 and yields a same improvement.

EXAMPLE 3 Production of a heat-sensitive material with built-in infrared material A composition consisting of 10 g. of a dispersion of 13 g. of Prussian blue in 300 g. of a 4.5% aqueous gelatin solution, 10 g. of a 12% aqueous solution of saponine, and 10 g. of a 2.5% aqueous solution of the sodium salt of the condensation product from oleic acid and methyl-- taurine is applied to a gelatin-coated cellulose triacetate support pro rata of 130 g. per sq. 111.

After solidification, the resulting material is coated with a second layer pro rata of 36 g. per sq. m. from the following composition:

The material is then dried with an air-stream at 30 C. When copying an original having coloured image areas with the resulting material, almost no difference in watersolubility or permeability for water or aqueous ink can be distinguished between the image parts of different colour. A similar material comprising no Prussian blue in the lower layer, reproduces the coloured image parts, especially the blue ones, considerably less favourably.

EXAMPLE 4 A heat-sensitive material as described in the abovementioned Belgian patent specification 657,5 2, filed Dec. 23, 1964 by Agfa A.G. is processed as defined therein. The original is a copy that comprises red image areas absorbing almost no infrared radiation and black image areas absorbing the infrared radiation very well.

Black lines having the same width are reproduced too broadly on the copy (under-exposure), whereas red lines are reproduced too narrowly (over-exposure). It is impossible to find an average exposure time at which both lines can be reproduced almost truly.

If the glass cylinder of the exposure apparatus is changed in such a way that the infrared radiation in the copying light is absorbed essentially, a true copy is obtained without diificulties. For carrying out the process of the invention the following alterations may be introduced in the glass cylinder of the exposure apparatus:

(1) Instead of a glass cylinder of normal glass, an infrared-absorbing glass e.g. as made available by Deutsche Spiegelglas AG under the name URO' H9, is used.

(2) A glass cylinder of normal glass is used, but the inner side thereof is provided with a refiex coating re- :fiecting infrared radiation and transmitting visible light only 50% of the surface thereof is used for the exposure of the copying material. The other 50% of the surface is provided at the inner side with a reflex-coating reflecting only visible light but transmitting infrared radiation. Such coatings are used in cine-projecting apparatuses. In this way only 50% of the infrared" radiation originating from the flash-light is eliminated from the radiation effecting the copying.

(4) The flash-light is provided with a second casing tube filled with a solution absorbing infrared radiation, occasionally in a circuit that can simultaneously be used for cooling purposes. Such liquids are known and sometimes only an aqueous solution of copper sulphate suifices.

Reflex coatings are described e.g. in Warmeisolation von Na-Dampfiampen by R. Groh and 'E. Kaner in Unsere Forschung in Deutschland Philips Zentrallaboratorium Gm-bH Aachen/Hamburg 1964, page 40.

Layers reflecting infrared radiation and transmitting visible light are e.g. gold layers having a thickness of A. or tin dioxide layers having a thickness of 3.2 A.

What we claim is:

1. In a method of reproducing an original bearing graphic information in a plurality of different colors which absorb infrared radiation in differing degrees, wherein a thermographic recording layer adapted when exposed to a pattern of heat to produce therein an image of said pattern and having substantially uniformly distributed therethrough at least one substance which absorbs visible radiation and converts the same into heat, has impinged thereon a pattern of radiation remaining after said original has been uniformly exposed to a source of radiation emitting a mixture of infrared and visible radiation and has absorbed said radiation in the graphic areas but not in the background areas, the improvement which comprises filtering at least a major portion of said infrared radiation from the radiation to which said original is exposed.

2. Process according to claim 1, wherein infrared radiation has been eliminated from the light used for the exposure by a filter, which is substantially transparent for radiation with wavelengths below 800 m and which is placed between the light source and the original.

3. Process according to claim 1, wherein a copying material is used having a recording layer comprising gelatin as a binder and finely divided silver or carbon as a pigment capable of absorbing visible light and converting it into heat energy.

4. Process according to claim 1, wherein use is made of a copying material comprising at least one layer having incorporated therein particles composed wholly or mainly of a hydrophobic thermoplastic polymer as a dispersion in a hydrophilic binder in a ratio greater than 1:1 by weight, these particles being in heat-conducting relationship with one or more substances, which absorb electromagnetic radiation in at least a part of the wavelength range of said radiation and convert the corresponding part of said radiation into heat.

5. The method of claim 1 wherein substantially the entirety of said infrared radiation is filtered from the radiation to which said original is exposed.

References Cited UNITED STATES PATENTS 2/1964 Roman et a1 1l71.7 X 1/ 1967 Gaynor 9627 

